1. Field of the Invention
The present invention relates to a method and apparatus for fine pattern forming. Particularly, the present invention pertains to a fine pattern forming apparatus for forming a fine pattern formation while applying an elastic wave to a vacuum chamber.
2. Description of Related Art
FIG. 1 is a schematic cross-sectional view of a conventional fine pattern forming apparatus, e.g., a plasma etching apparatus. In this apparatus, a semiconductor substrate 2, in which a fine pattern is formed, is disposed within a vacuum chamber 1. The semiconductor substrate 2 has on its surface, for example, thin polycrystalline silicon film and a photoresist pattern mask which resists etching. In the vacuum chamber 1, the semiconductor substrate 2 is placed on a sample stage 4 which also serves as an electrode connected to a high-frequency power source 3 for supplying high-frequency power (hereinafter referred to simply as "an electrode 4"). An electrode 6 with gas nozzles 5 provided therein to uniformly supply an etching, i.e., reactive gas, e.g., chlorine gas, toward the semiconductor substrate 2 is disposed in opposed relation to the semiconductor substrate 2. The vacuum chamber 1 is provided with an evacuation port 7 through which the vacuum chamber 1 is evacuated and a reactive gas supply port 8 through which the etching gas is supplied into the vacuum chamber 1.
The thus-arranged conventional fine pattern forming apparatus will be operated in the manner described below. First, an etching gas is introduced into the interior of the vacuum chamber 1 from the reactive gas supply port 8 through the gas nozzles while the vacuum chamber 1 is evacuated from the evacuation port 7 by an evacuation means (not shown). Next, a high-frequency voltage is applied between the electrode 4 and the opposed electrode 6 by the high-frequency power source 3 to generate a glow discharge. In consequence, the etching gas introduced into the vacuum chamber 1 is activated and thereby becomes a plasma, generating active neutral molecules, neutral atoms and ions. Etching of the semiconductor substrate 2 progresses due to the presence of these molecules, atoms and ions, and a fine pattern is thus formed.
The above conventional fine pattern forming techniques has the following drawbacks.
(1) Uniformity of the etch rate
In the conventional techniques, since spatial distribution of the activated halogen gas or halogen ions occurs, when a fine pattern is to be formed on a sample having a large diameter, variation in the etch rate in the plane of the substrate occurs. A reduction in the etch rate requires a large etching chamber.
(2) Etching selectivity with respect to a base film
In the conventional techniques, an etchant such as charged particles is irradiated onto the sample in an accelerated state. In consequence, the etched surface is damaged and sufficient selectivity with respect to the base etching preventing film cannot be obtained.
(3) Reduction in the etch rate for a fine pattern due to the microloading effect
In the conventional techniques, since the directional property of an etchant is not satisfactory, the amount of etchant reaching a gap in a fine pattern is reduced, decreasing the etch rate. Furthermore, the degree at which a reaction product attaches to the side wall of a pattern formed during the etching depends on the pattern size. Dependence of anisotropic etching profile on the pattern size must be reduced.
(4) The above-described problems of the conventional techniques harm the characteristics of the active devices formed by the fine patterning.